The present invention relates to a memory system for computers, and more particularly to a disk array controller for controlling a plurality of disk drives arranged in an array for the parallel and simultaneous operations of the disk drives.
As an example of related arts of a disk array controller, there is known JP-A-2-236714 corresponding to U.S. Pat. No. 5,148,432. According to this related art, the disk array controller is connected to disk drives via small computer system interfaces (SCSI). In writing data with redundancy into a disk, the disk array controller divides data to be written into each of the sector. While each of data is sequentially being transferred via SCSI to different disk drives, redundant data is generated by using an error correcting code (ECC) engine.
With this related art, since data write is executed without synchronization between disk drives, there is a possibility of different timings between disk drives when data transferred from SCSI is actually written in the disk drives. Accordingly, if the operation of writing data into a plurality of disk drives in response to the same write request is interrupted by a power failure or the like, there occurs a phenomenon that data write has completed for some disk drives, but not for other disk drives. Therefore, if a host computer reads data from the region where some disk drives have been written with data and other disk drives have not been written with data and still has past data, the read data contains both the write completed data and past data, resulting in transferring inconsistent data to the host computer. Data not actually written that is read by the host computer is called data distortion. This phenomenon should be avoided by all means, with respect to auxiliary storage units of a computer system.